With the rapid increase in communication speed and spread of high capacity storage media and various portable multimedia reproducing apparatuses, demand for digital media contents has increased. Thus, various media contents providers have appeared and provide the media contents by using various methods. However, due to characteristics of the digital media contents, a copy, which is the same as the original digital media contents or is modified from the original digital media contents, may be easily made and also easily distributed through various routes. Thus, commercial damage to providers providing the digital media contents and producers making the digital media contents has rapidly and substantially increased.
As the distribution of digital media contents through the Internet has become common since a high speed communication network is widely distributed in general homes, formats of digital media files have been developed in various directions in order to provide, with a smaller capacity or a strengthened real time transmission function, media contents having higher quality. These formats of various digital media files have been developed to add various functions concerned with raising or maintaining quality of the digital media contents or strengthening a streaming function for real-time transmission according to Internet transmission characteristics. Even in the case of a format having no regard for the streaming function, a technology for transmitting the format in a streaming method has been accomplished and thus most of the currently used digital media contents may be streamed through a streaming system.
Streaming of the digital media contents is widely used as a way to protect the digital media contents because the streaming of the digital media contents has not only a real time characteristic in which reproduction is started together with contents selection but also a contents security characteristic depending on a method of reproducing the contents while storing the contents in a memory by dispersing and transmitting the contents in units of packets and then of deleting contents whose reproduction is completed, from the memory.
FIG. 1 illustrates a configuration of a streaming system providing general digital media contents by using the streaming method. As illustrated, the streaming system includes a contents server 1 including contents, a streaming server 3 which is connected to the contents server 1 through a LAN network 2, requests the contents server 1 to send the contents, and transmits received contents in units of packets, and a user terminal 5 which is connected to the streaming server 3 through Internet 4, requests the streaming server 3 for the contents, and reproduces the contents received in units of packets.
An operation of the system is described below.
First, if the user terminal 5 requests desired contents by accessing the streaming server 3 through Internet 4, the streaming server 3 receives the contents from the contents server 1 by requesting the contents server 1 to send the contents, and then provides received contents to the user terminal 5 in units of packets. The user terminal 5 reproduces the contents streamed in units of packets through an internal reproducing unit 6, and then a packet, reproduction of which is completed, is deleted.
Since this streaming server 3 provides a streaming service while being connected to a plurality of user terminals, session information, such as a packet size depending on connected ports when contents are being provided and a communication status, is constantly changing. In addition, although the streaming server 3 may have a security characteristic, in that packet information is deleted after reproduction of the packet information is completed, it is difficult to ensure security through an existing streaming system such as the streaming system of FIG. 1, because a received packet may be stored, in a file form, in a network terminal or the user terminal 5 and, in some cases, a contents file may be directly accessed by determining the contents location in the contents server 1.
A server using a digital rights management (DRM) technology has been developed to protect the digital media contents. However, in the case of using a basic method in which the digital media contents may be reduced by encoding all of the digital media contents and decoding the encoded digital media contents through a specific license, it is difficult to apply the streaming service to the basic method, and reproduction has to be performed after receiving total contents having a large capacity and then decoding the total contents.
Meanwhile, in the case of applying a packager for contents packet encoding to a back end of the streaming server, an existing system may be used. However, in this case, speed is slow because an encoding process is included in a streaming process, a possibility of original contents being leaked still exists, and, in addition, a streaming function may not be smoothly performed.
In order to partially solve this problem, in Korean Patent Application No. 2010-0596382, entitled “Apparatus for Protecting Digital Content and Method Therefor”, a technology, in which a streaming service is implemented through an existing streaming server, has been provided. In this technology, the streaming service provided through an existing streaming server is made possible by maintaining a format of a MP4 file, with disposing a packager between a contents server and a streaming server and thus selectively encoding only video and audio data streams of the MP4 file. This technology is described below with reference to FIG. 2.
FIG. 2 illustrates an example of a configuration of a streaming system for streaming MP4 digital media contents while protecting the digital media contents. The streaming system of FIG. 2 includes a streaming server 13 and a user terminal 15, which have the same functions as those of the existing art, a packager 11, which is disposed between a contents server 10 and the streaming server 13, for encoding the digital media contents to use the DRM technology, a user terminal 15 of which a reproducing unit 16 includes a DRM filter 17 for securing a DRM license and decoding by using the DRM license, and a DRM server 20 for generating a license depending on packaging information of the packager 11.
In the streaming system, as illustrated in FIG. 2, if the contents server 10 provides contents requested by the streaming server 13, the packager 11 packages the contents by considering a set-up of a session between the user terminal 15 and the streaming server 13 and then provides packaged contents to the streaming server 13. Here, the packager 11 provides packaging information to the DRM server 20. The streaming server 13 performs streaming by using encoded contents which are generated by compressing, for example, only a key-frame of a video signal or more data including the key-frame. The reproducing unit 16 of the user terminal 15 receives a streamed encoded packet, namely the encoded contents, and the DRM filter 17 of the reproducing unit 16 requests the DRM server 20 to send a license, based on session information which is currently being accessed and described in session description protocol (SDP) format information including information about an environment for communicating with the streaming server 13 (namely, communication port information) and contents information (namely, contents identifier). The DRM server 20 retrieves packaging information stored in the packaging information storing unit 21 with the session information, and, if there is corresponding information, a license generating unit 22 generates a license and then provides the license to the DRM filter 17. The DRM filter 17, which obtains the license from the license generating unit 22, decodes a received packet, and the reproducing unit 17 reproduces a decoded packet. The received packet is deleted after a reproduction is finished.
That is, the streaming system illustrated in FIG. 2 newly performs packaging for only a currently connected terminal during a streaming service, stores information, which is related to encoding applied to corresponding packaging, in the DRM server 20 based on the current session information. In addition, if the DRM filter 17 receiving the encoded packet requests the DRM server 20 to send a license based on the current session information, the DRM server 20 searches for encoding-related information stored based on the current session information and then issues a corresponding license.
In the streaming system of FIG. 2, if the encoded packet is stored in a separate file 18, a corresponding file is not normally reproduced because at least a portion of a data part is encoded. Meanwhile, because the obtained license depends on one-time information such as a communication session of the streaming server 13 and the user terminal 15, it is impossible to obtain again license information after a session connection is ended, and thus it is impossible to reuse the obtained license.
Although the streaming system illustrated in FIG. 2 may use an existing streaming server, reduce an encoding time, and raise security by managing a license based on the one-time information, in the streaming system of FIG. 2, only a single format may be used due to the fact that encoding should be performed all the time for every connected user, a portion of the contents may be obtained because encoded information may be restrictively used to reduce load, and there exists a serious security problem in which illegal access that could enable downloading of the contents by obtaining addresses of the contents stored in the contents server 10 is not blocked. In addition, in the streaming system of FIG. 2, because it is necessary to newly encode contents and then transmit whenever a user terminal requests the streaming server to send the contents, the number of users capable of being simultaneously connected is limited. In addition, because it is impossible to reuse the digital media data received through a large amount of time and network traffic, all processes should be repeated from the first if the user wants to view the same contents again. Also, it is impossible to reproduce and reuse the contents by moving received contents to a portable multimedia reproducing apparatus or transmitting the received contents to another person and then additionally obtaining only a license.
Accordingly, new technology for protecting contents, which may be applied to various contents formats and also maintain compatibility with an existing contents distribution system, which may maximize security without reducing the number of simultaneously connected users or increasing a separate service providing system load, and which may reuse the contents by re-obtaining only a license after transmitting encoded contents to another person or moving the encoded contents to another apparatus while making it possible to reuse received contents, is required.